Handling of soluble IgA aggregates by the mononuclear phagocytic system in mice. A comparison with IgG aggregates

We have studied the fate of soluble stable aggregates of human IgA (A-IgA) and IgG (A-IgG) after their injections in mice, as well as in vitro catabolism by liver, kidney and peritoneal macrophages. The half-life of the fast component of blood clearance was similar for both aggregates. However the half-life of the slow component of A-IgA clearance was significantly slower than A-IgG (t1/2 10 . 03 v. 7 . 52 hr, respectively). The A-IgA deposited in liver and kidney was removed significantly more slowly than A-IgG. Studies in isolated liver and kidney slices suggest that this could be due to the impaired catabolism of A-IgA as opposed to that of A-IgG. Interestingly the kidney hardly participates in the processing of A-IgA. At the three doses employed (1, 5 and 10 micrograms of both aggregates) peritoneal macrophages bound and catabolised significantly less amount of A-IgA than A-IgG. Complement seems to have no role in the processing of A-IgA by peritoneal macrophages unlike that observed with A-IgG. It is suggested that the impairment in handling of A-IgA by the mononuclear phagocytic system could provoke their persistence in the circulation and deposition at sites susceptible to injury. These results may be of some relevance for the understanding of physiological IgA-IC (immune complex) clearance and for the pathogenesis of IgA-related diseases.